Beam splitters are fundamental components in lasers, cameras, microscopes, telescopes, and even the gravitational wave detectors that confirmed Einstein's predictions about spacetime. A beam splitter (or beamsplitter, power splitter) is an optical device which can split an incident light beam (e. a laser beam) into two (or sometimes more) beams, which may or may not have the same optical power (radiant flux). It is a crucial part of many optical experimental and measurement systems, such as interferometers, also finding widespread application in fibre optic telecommunications. One portion passes through the device while the other reflects off it, and the ratio between the two can be controlled by design.